[SOLVED] ESC wiring clarification

I am wanting a bit of clarification on the documentation on this page: http://docs.emlid.com/navio2/Navio-APM/hardware-setup/

In particular, the snippet:
"Only one ESC power wire (central) should be connected to Navio2 servo rail, otherwise BECs built in ESCs will heat each other."
Out of each of my 4 ESCs I have a servo cable with 3 wires: Yellow, Red, Black. It looks like to me they are pulse, + and - respectively.
Is the documentation telling me that I should remove the Red (+) and Black (-) wires from all but ONE of my servo cables that plug in to my Navio?

Photo of said ESC servo cable here: https://drive.google.com/file/d/0B6dT7W9NhU2vbEtsZFVubVdua2M/view?usp=sharing

Yep, I’m also confused about exactly the same thing.

Although the “servo rail” doesn’t need power for the ESCs themselves, if you have RC input (strongly recommended) or any other devices that want power from ADC, RC or PWM/servo 1-13 connectors you will need to connect something with +5v there. But only one 5v input, hence the warning.

As it’s common for ESCs to have BECs this means you have 4 times 5v input (on a quadcopter, 8 on an octocopter) which cannot be connected together without special circuity to prevent overload. The BEC components will overheat each-other as documented.

Just disconnect all but one of the red wires from the ESCs and tape back or use directly for other purposes (as they have a common ground that is okay).

Personally I prefer to buy opto ESCs, which have no BEC, first to reduce interference and second to save a little weight. Then I buy a PDB with a 5v (and 12v when I want a live FPV transmitter) or install a separate BEC.

Also be aware of the amperage rating of the chosen ESC or BEC’s output. It will most likely be enough for Navio but if you hang a load of USB devices and WiFI dongles with the “max_usb_current” option you will need a separate BEC with a higher rating.

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I thought I would update this thread with my experience-

I connected my Radio Rx to the PPM input of the Navio. No problem. All working and with power.
I removed the Red + wires from all but one of the ESCs. Which I thought was the recommendation in the documentation.
As soon as I connected ESC #1 (the one with the + wire) the power to my Navio would drop out. But my ESCs were powered
I ended up removing the Red + wire from ESC #1 as well (so NONE of the Red + wires from ESCs were connected to Navio) and the power to my Navio stayed on and my ESCs were all powered. I have throttled up my drone successfully and all seems well.

The ESCs I am using are Multistar 20A Flashed with SimonK.

I have been flying my drone for a few weeks now with none of the red wires connected to the Navio as described in my previous post.

Now I have built a servo controlled gimbal and need to power 2 servos. I decided to connect back in the red wire from the ESC that powers my #4 motor. That is the only one I connected.

Unfortunately I have the problem described in my previous post- when I connect any one of the red wires from my ESCs my Navio does not power up.
Any suggestions about why this would be? And what I can do to power my servos? Ideally I don’t want to buy a BEC as my ESCs have BECs in them and I’d like to be able to utilise them

@Bradley_Scott Could you please measure the voltage on those red wires? Also, what is the current rating of BECs in your ESCs?

Ah. That identified my problem. Looks like my ESCs aren’t as advertised. They are passing through the entire voltage from my battery. The red wire voltage was nearly 12v

I guess my options are:

  • Buy a BEC and connect that in to my battery.
  • Swap out my ESCs with the ones I thought these ones were: Multistar 20A ESCs with 5v 4A BECs

Any other suggestions for how I could step down the voltage?

I think that separate 5V BEC should be the easiest solution here.